Superduty axle swap
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The_Josh_Bear
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I don't remember the numbers but it comes down pretty fast with different rear ends. There's another thread not too old that shows Ford's limits by axle ratio.
How much do you tow?
Legal towing capacity has a lot to do with if you have an F250 or F350, and then it's up to your state regulations after that.
But practically speaking, you will be able to tow most things ok with the change-- though I see you're in Colorado and that will have a stronger affect on towing if you're in the Rockies.
If you're talking 4-5k mostly flat you're OK. Maybe some good hills once in a while. My towing ability is just ok since I went from 4.10 stock tires to 3.55 and 33's. With my turbo setup running well it tows my 4k trailer just fine until I start going over Snoqualmie pass and then my coolant overheats. (Which isn't necessarily a gearing problem) I'm also right at 1200* EGT, maxed out stock IP and after-cooled.
I've had this setup for a couple years now and I am still getting used to the long gears...!
My point is even with 3.73 and 35s you'll have a little more gear advantage than me and if you tow heavy in the Rockies I would say not to change the gearing.
Maybe just change the tires and give it hell up the worst grade you can find and see how you like it.
How much do you tow?
Legal towing capacity has a lot to do with if you have an F250 or F350, and then it's up to your state regulations after that.
But practically speaking, you will be able to tow most things ok with the change-- though I see you're in Colorado and that will have a stronger affect on towing if you're in the Rockies.
If you're talking 4-5k mostly flat you're OK. Maybe some good hills once in a while. My towing ability is just ok since I went from 4.10 stock tires to 3.55 and 33's. With my turbo setup running well it tows my 4k trailer just fine until I start going over Snoqualmie pass and then my coolant overheats. (Which isn't necessarily a gearing problem) I'm also right at 1200* EGT, maxed out stock IP and after-cooled.
I've had this setup for a couple years now and I am still getting used to the long gears...!
My point is even with 3.73 and 35s you'll have a little more gear advantage than me and if you tow heavy in the Rockies I would say not to change the gearing.
Maybe just change the tires and give it hell up the worst grade you can find and see how you like it.
frankenwrench
overkill is under rated!
When I had 4.10 gears and 37s I had no issue towing 14-17k. I also live in Texas...... I now have 33s and an 01 SD rear end with 373 gear and I notice no differance in towing or rpms. Not exactly apples to apples as far as your question is concerned, but fairly closish
Thank you, @The_Josh_Bear & @frankenwrench. Exactly what I needed to hear.
I believe you will be very disappointed in that combination. The 35's give you the look, but kill the power of the truck. With 3.73's and 35 inch tires, you will be downshifting on steep hills EMPTY with nothing in the bed and not towing anything. I see you live in Colorado, so I would imagine you have some steep inclines there.
That is your key right there...
Remember,
The 7.3 PSD was 235ish stock..... and the 6.0 was 325..... I have an 03 6.0 Excursion with 3.73's. I tow a 4000lb travel trailer like nothing, with the cruise set at 70..... but... I am 100% factory... 31 inch factory height tires, and no tuner so still at ~325/560 which gives me 70 @ ~2000rpm
What year superduty axles are you looking at? Gas trucks had deeper gearing usually. 4.10-4.30. My '07 set are 4.10.
One thing with 3.73 that's missed is its closer to 3.54 than 4.10 (do the math). I suspect you'll be relying on a lower gear in the ZF more of the time.
Legal towing is really about your jurisdiction. In mine, its about paying enough money in red tape to cover your total gross... and then also having a high enough rating hitch and tires for the load; without exceeding the truck's GVWR. If the factory tow rating was a real rating (and not a guideline) it would be on the same decal as the GVWR.
One thing with 3.73 that's missed is its closer to 3.54 than 4.10 (do the math). I suspect you'll be relying on a lower gear in the ZF more of the time.
Legal towing is really about your jurisdiction. In mine, its about paying enough money in red tape to cover your total gross... and then also having a high enough rating hitch and tires for the load; without exceeding the truck's GVWR. If the factory tow rating was a real rating (and not a guideline) it would be on the same decal as the GVWR.
@snicklas - I keep it around 60 even on the highway. It's too loud otherwise. And i spose I could give it a little more fuel, but with everything else stock, I have my doubts that i would use it...even with the banks.
I need to be able to tow around 7K while also hauling another 1K in the bed, and doing this offroad while at it.
@u2slow - I'm looking for 99-04 D60 and I'll match it up with a 10.5 in the rear while I'm at it.
I need to be able to tow around 7K while also hauling another 1K in the bed, and doing this offroad while at it.
@u2slow - I'm looking for 99-04 D60 and I'll match it up with a 10.5 in the rear while I'm at it.
The_Josh_Bear
Full Access Member
What are you towing that has 35in wheels to match for ground clearance?? 
If you want more power from the setup you already have then go with an aftercooler, it's the best power mod I've done after the turbo and it's not close.
Towing 7k off road will not be hard with taller gears and bigger tires so that's not really a worry. It's more about speed limits and grades and gear selection.
If you want more power from the setup you already have then go with an aftercooler, it's the best power mod I've done after the turbo and it's not close.
Towing 7k off road will not be hard with taller gears and bigger tires so that's not really a worry. It's more about speed limits and grades and gear selection.
The 35s don't have to "match" what I'm towing. They're simply for more clearance when offroading.
I've considered after cooling as well and in fact just read through this entire thread this past week...the money quotes being here. Not that I would do exactly that but it was interesting since we have the same turbo.
I've considered after cooling as well and in fact just read through this entire thread this past week...the money quotes being here. Not that I would do exactly that but it was interesting since we have the same turbo.
The stock 235/85/16 is 31.73" I went to a 255/85/16 which is 33.07" This was a larger increase than you may think. First gear now has a purpose and makes the truck acts more like it should have been from the factory. I have the 4.10's and 4wd and zf5. I don't want to say don't do it but you may regret going to 35's and 3.73's if towing up and down hills.
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Nice looking pickup @SirRea63l.
Though mine are 16.5", I think we have the same wheels.
Though mine are 16.5", I think we have the same wheels.
Thanks, they were budget friendly American Racing AR62 Outlaw II in a 16x8. Going to the slightly larger diameter tires was one of the best things I have done for drivability of the truck, I am glad I did not go any larger. I don't work this this truck but the overall gearing change from larger diameter wheels worked perfect, larger ones may have been too much in my case.
The_Josh_Bear
Full Access Member
Nice I have that same cooler in plain aluminum. If you still have A/C you might consider using 2.5in pipes instead of 3". I don't have working A/C and 3" was still a pain. (Have the compressor still mounted but no belt or hoses).
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